DESCRIPTION (APPLICANT'S ABSTRACT): Low-carbohydrate, high-fat, high-protein diets promoted by books, the Internet and other media are among the most enduring weight-loss diets in the US and Europe. The public favors these diets because they include popular energy-rich foods like meat and cheese while at the same time promising to produce rapid weight loss. Without an evidence-based understanding the consequences of these diets, health care providers may find it difficult to evaluate these diets in advising clients who are choosing to use them to reduce weight in large numbers. The goal of this pilot project is to establish methodology for studying these diets in a clinical trial setting. A group of 24 overweight participants with BMIs between 27 and 39.9 Kg/m~ will be studied in a parallel group design for six weeks of controlled feeding and six weeks of follow-up. After screening, participants will be allocated to either a low-carbohydrate diet similar to the one marketed by Dr. Robert Atkins, or to an energy-matched, high carbohydrate, low fat diet similar to the combination diet used in the DASH study for six weeks. Participants will receive all foods and beverages in the General Clinical Research Center at Oregon Health Sciences University during the controlled feeding phase. Participants will first consume a standard American diet for one week to stabilize their energy requirements and acclimate to the demands of the study. This run-in week will be followed by a six-week period when participants consume either the Atkins diet or the DASH diet. Follow-up consists of following these same diets in the home setting for an additional six weeks. Measures of interest include markers of oxidative damage, cardiovascular disease (CVD) risk (lipids, blood pressure insulin, glucose), bone health, energy expenditure, substrate utilization and body composition. We will also conduct focus groups and individual interviews during the period when participants follow these diets at home to gain an understanding of how these diets affect the quality of their lives. This study will provide us with many tools to evaluate a variety of ways that low-carbohydrate weight-loss diets affect adherence, body weight and body composition, energy metabolism, and several markers of chronic diseases which may be affected by the altered nutrient intake. It will provide insights as to the nature of these changes, the time course of the changes, and variability of these measures. We will use information gained in this pilot study to design more comprehensive studies that evaluate these alternative diets in a more rigorous fashion.